(1) Field of the Invention
The present invention relates to an apparatus for controlling an object of control in an electronically controlled internal combustion engine while learning variations of the driving state of the engine with the lapse of time.
More particularly, in an electronically controlled internal combustion engine provided with fuel injection means which is opened and closed in an on-off manner by a driving pulse signal of electronic control means or with an idle speed control valve for determining the opening degree of a passage bypassing a throttle valve arranged in an intake passage by minute oscillation in the opening or closing direction according to said driving pulse signal, the present invention relates to an apparatus for learning and controlling the fuel injection quantity or the quantity of air passing through the bypassing passage at the time of idling.
(2) Description of the Prior Art
An electronically controlled fuel injection valve is opened by a driving pulse signal (injection pulse) given synchronously with the rotation of an engine and while the valve is opened, a fuel is injected under a predetermined pressure.
Accordingly, the injection quantity of the fuel depends on the period of opening of the valve, that is, the injection pulse width. Assuming that this pulse width is expressed as Ti and is a control signal corresponding to the injection quantity of the fuel, Ti is expressed by the following equations: EQU Ti=Tp.times.COEF.times..alpha.+Ts and Tp =K.times.Q/N
wherein Tp stands for the injection pulse width corresponding to the basic injection quantity of the fuel, which is called "basic fuel injection quantity" for convenience, K stands for a constant, Q stands for the flow quantity of air sucked in the engine, N stands for the rotation speed of the engine. COEF stands for various correction coefficients for correcting the quantity of the fuel, which is expressed by the following formula: EQU COEF=1+Ktw+Kas+Kai+Kmr+Ketc
in which Ktw stands for a coefficient for increasing the quantity of the fuel as the water temperature is lower, Kas stands for a correction coefficient for increasing the quantity of the fuel at and after the start of the engine, Kai stands for a correction coefficient for increasing the quantity of the engine after a throttle valve arranged in an intake passage of the engine is opened, Kmr stands for a coefficient for correcting the air fuel mixture, and Ketc stands for other correction coefficient for increasing the quantity of the fuel, .alpha. stands for an air-fuel ratio feedback correction coefficient for the feedback control (.lambda. control), described hereinafter, of the air-fuel ratio of the air-fuel mixture, and Ts stands for the quantity of the voltage correction for correcting the change of the flow quantity of the fuel injected by the fuel injection valve, which is caused by the change of the voltage of a battery.
In short, the desired injection quantity of the fuel is obtained by multiplying the basic fuel injection quantity Tp by various correction coefficients COEF, and when a difference is brought about between the aimed control value to be attained by the control and the actual controlled value, this difference is multiplied by .alpha. to effect the feedback control and the correction for the power source voltage is added to the feedback control.
This air-fuel ratio feedback correction control is disclosed in, for example, U.S. Pat. Nos. 4,284,050, 3,483,851 and 3,750,632.
However, in this air-fuel ratio feedback control, for example, when one constant driving region is greatly changed to a different constant driving region, if the base air-fuel ratio in this different stationary driving region is greatly deviated from .lambda.=1 (.lambda. stands for an actual air-fuel ratio), it takes too long a time to perform the feedback control (proportion and integration control . . . PI control) of the change of the base air-fuel ratio generated by this deviation to .lambda.=1. More specifically, even though the base air-fuel ratio has been obtained from the specific injection quantity Tp.times.COEF and the deviation of this air-fuel ratio from the theoretical air-fuel ratio has been corrected by the PI control based on .alpha., since the base air-fuel ratio is greatly changed, the base air-fuel ratio is controlled to a value greatly different from .lambda.=1 if Tp.times.COEF used up to this time is still used, and the feedback correction by similar PI control should be performed and it takes a long time to correct the base air-fuel ratio to .lambda.=1 by the feedback correction.
A control system in which the above-mentioned disadvantage is eliminated by learning the control quantity controlled by the system and increasing the respondency of the air-fuel ratio control in the same driving state has been proposed by us in Japanese Patent Application Laid-Open Specifications No. 203828/74 and No. 203829/74 and U.S. Patent Application Ser. No. 604,025, filed Apr. 26, 1984, now U.S. Pat. No. 4,615,319.
According to this control system, learning control of the air-fuel ratio feedback control is first carried out. More specifically, in the air-fuel ratio feedback control region, if the base air-fuel ratio is deviated from the aimed air-fuel ratio .lambda.t, since the feedback correction coefficient .alpha. is increased for compensating this gap during the process of transfer, the driving state at this time and .alpha. are detected, and a learning correction coefficient K1 based on this .alpha. is determined and stored. When the same driving state is brought about, the base air-fuel ratio is corrected to the aimed air-fuel ratio .lambda.t with a good respondency by the stored learning correction coefficient K1. Storing of the learning correction coefficient. K1 is performed for all of engine-driving state areas of a predetermined range formed by lattice division of a map of RAM according to the rotation speed of the engine and the engine-driving conditions such as the load.
More specifically, the map of the learning correction coefficient K1 corresponding to the rotation speed of the engine and the driving conditions of the engine such as the load is formed on RAM, and when the injection quantity Ti is calculated, the basic injection quantity Tp is corrected by K1 as shown by the following equation: EQU Ti=Tp.times.COEF.times.K1.times..alpha.+Ts (1)
Learning of K1 is advanced according to the following procedures.
(i) The engine-driving state in the constant state and the median .alpha.c of control of .alpha. (the mean value of a plurality of values K1 at the time of reversion of increase and decrease of the output signal of an O.sub.2 sensor) are detected.
(ii) The value K1 (old) heretofore learned, corresponding to the engine-driving state, is retrieved.
(iii) The value of K1(old)+.DELTA..alpha./M is determined from .alpha.c and K1 (old), and the storage is renewed with the obtained value (learned value) being as new K1(new).
Incidentally, .DELTA..alpha. stands for the deviation from the standard value .alpha.1 and expressed by .DELTA..alpha.=.alpha.-.alpha.1. The standard value .alpha.1 is ordinarily set at 1.0 as the value corresponding to .lambda.=1. M is a constant larger than 1.
However, in this conventional learning and control apparatus for an internal combustion engine, with increase of the frequency n of learning, the learning correction coefficient K1 is sequentially renewed to K1+.DELTA..alpha./M based on the preceding learning correction coefficient, and therefore, learning is advanced while the new learning correction coefficient is restricted by the preceding learning correction coefficient. Accordingly, if the injection quantity under the same driving conditions is abruptly changed on standing or by exchange of parts, learning cannot catch up with this change and the frequency of learning for obtaining a proper learning correction coefficient after the change is increased and a considerably long time is necessary for effecting learning over the entire region, and during this period, the exhaust characteristics are degraded.
Also in the apparatus disclosed in Japanese Patent Application Laid-Open Specification No. 211738/84, there arises the problem mentioned above in connection with learning and control of the fuel injection pulse width. According to this known technique, an idle control valve is disposed in an auxiliary air passage bypassing a throttle valve, and the opening degree of the idle control valve is adjusted according to the duty ratio of a pulse signal. The preset aimed rotation speed is compared with the actual rotation speed and feedback correction is effected, and a learning correction quantity stored in RAM in correspondence to the rotation speed is retrieved from the actual rotation speed. The weighted mean of the feedback correction quantity and the learning correction quantity is calculated, and the data in RAM are renewed by using this mean value as a new learning correction coefficient, and the above-mentioned feedback correction quantity and learning correction quantity are added to the preset basic control value of the pulse signal to operate the control value of the pulse signal for controlling the idle control valve. As in case of learning and control of the fuel injection pulse width, learning cannot catch up with an abrupt change of the control quantity in case of learning and control of the learning correction quantity.